The present invention relates to a process for producing a semiconductor device, and more particularly, it relates to a film formation process of an interlayer insulation film of multilayer interconnection.
A silicon nitride film or a silicon oxinitride film (hereinafter referred to as a silicon nitride series film) formed by a capacity coupling type plasma CVD process has been industrially used as a dielectric film of a semiconductor device. The film formation is conducted under such conditions that the gas flow rate ratio of SiH4, N2 and NH3, which are reaction gases, SiH4:N2:NH3 is 1:1xcx9c50:1xcx9c10, and the processing temperature is about 400xc2x0 C. or lower. The film formation conditions are disclosed, for example, in U.S. Pat. No. 5,336,640. The film contains a large amount of hydrogen in the film, and when the step subsequent to the film formation step is conducted at a temperature higher than that of the film formation step, the hydrogen contained in the film is released to adversely affect the electric properties of the semiconductor device. Therefore, the application of the film is mainly a final passivation film of a semiconductor device. (The application shown in the U.S. Patent is those for a final passivation film.)
On the other hand, in order to solve the problem of increasing interconnection""s RC delay (which is proportional to the product of the interconnection resistance and the capacity between interconnections) associated with fine structures of a semiconductor device, as interlayer insulation film, the use of an SiOF film formed by doping a conventional silicon oxide film with fluorine or a siloxane series film having a low dielectric constant containing a methyl group is examinated for reducing the interconnection capacity. A high quality SiOF film formed by a dual frequency excited capacity coupling plasma CVD is disclosed in xe2x80x9cWater Absorption Properties of Fluorine-Doped SiO2 Film Using Plasma-Enhanced Chemical vapor Depositionxe2x80x9d, Japanese Journal of Applied Physics, vol. 35, No. 12A, p. 6217-6225 (1996) incorporated herein for reference. This discloses that an SiOF film having a low dielectric constant exhibiting no water adsorption with the lapse of time is formed by a conventional plasma CVD apparatus at a relatively high temperature of about 470xc2x0 C.
However, because a conventional aluminum (Al) interconnection cannot withstand at a high temperature of 470xc2x0 C., the SiOF film has not been applied to a semiconductor device using the Al interconnection.
Thus, in order to reduce the-RC delay, a copper (Cu) interconnection having a lower resistance than Al is being used. The Cu interconnection has higher heat resistance than Al and can be used as an interlayer insulation film. The Cu interconnection is formed in such a manner that a groove pattern is formed on an interlayer insulation film, and the Cu interconnection is buried in the grooves (i.e., a damascene process). The formation of the groove pattern on the interlayer insulation film is conducted by anisotropic etching using reactive ion etching (RIE). The use of the silicon nitride series film formed by the plasma CVD as an etching stopper layer for RIE is being considered.
The silicon nitride series film formed by plasma CVD is also used as an anti-reflection film in a lithography process for preventing reflection of exposure light at a lower part of a resist to conduct fine fabrication with high accuracy.
The silicon nitride series film can also be formed by thermal CVD. Although the film cannot be used as an interlayer insulation film after the formation of Al or Cu since the film formation temperature is 700xc2x0 C. or higher, it has been applied to an etching stopper layer for an interlayer insulation film as the first layer directly on the semiconductor device, which is subsequently subjected to a heat treatment step.
In the case where the conventional silicon nitride series film by plasma CVD is formed as the etching stopper layer for RIE on formation of the interconnection grooves or the anti-reflection film, when an SiOF film formed at a relatively high film formation temperature (470xc2x0 C.) is formed on the silicon nitride series film, hydrogen contained in the silicon nitride series film is released to deteriorate the adhesion of the film, so as to cause detachment of the film. The detachment of the film causes a short-circuit or connection failure of the interconnection of the semiconductor device containing the part of detachment, and thus brings about deterioration of the yield.
On the other hand, the silicon nitride series film formed by thermal CVD contains substantially no hydrogen, but in the case of a device having a fine gate length of 0.18 xcexcm or less, the diffusion control of the impurity layer becomes difficult due to the heat load at the temperature of 700xc2x0 C. or higher. In such a case, the reliability of the semiconductor device is considerably decreased, for example, by causing scattering in operation voltage of the semiconductor device.
Therefore, an object of the invention is to provide a process for producing a plasma silicon nitride series film having a low hydrogen concentration with a small heat load.
Another object of the invention is to form a silicon nitride series film having high reliability with an yield that is not decreased.
In order to accomplish the objects, a method of the invention consists of following steps.
The method for producing a silicon nitride series film on a material to be treated using a plasma CVD apparatus having a reaction chamber evacuated to vacuum, comprising the steps of:
introducing a monosilane gas (SiH4) and a nitrogen gas (N2) as raw material gases into the reaction chamber at prescribed flow rates; and
subjecting the material to be treated to a heat treatment at a prescribed temperature,
the flow rate of the nitrogen gas being at least 100 times the flow rate of the monosilane gas.
The silicon nitride series film may be specifically SiN:H or SiON:H.
The prescribed temperature is preferably from 390 to 600xc2x0 C.